Genetic testing and diagnosis of infectious diseases play an important role in the field of clinical microbiology. To overcome the bias and limitations inherent with culture-based methodologies, genetic testing is being increasingly used to detect microorganisms contained in a sample. In order that such genetic testing can be performed, cells need to be lysed to allow extraction of the DNA and/or the RNA from the microorganisms in a concentration as high as possible.
Zhongtang Yu et al., 2004, “Improved extraction of PCR-quality community DNA from digesta and fecal samples,” BioTechniques, Vol. 36(5):808-812, describe a method for isolating DNA from digesta and fecal samples. In the method, 0.25 g of a sample fluid taken from a cow's gastro-intestinal system, which is assumed to contain microorganisms, namely bacteria, is first of all mixed with 1 mL of a buffer containing 500 mM sodium chloride, 50 mM Tris hydrochloride, pH 8.0, 50 mM ethylenediaminetetraacetic acid, and 4% sodium dodecyl sulfate. Moreover, 0.4 g sterile zirconia beads are introduced in the sample fluid. The mixture thus obtained is subsequently oscillated by means of a Mini-BeadBeater™ in a sample tube for three minutes such that the beads destroy the cell walls of the microorganisms. In this process, the DNA contained in the cells is released. The buffer also serves to protect the DNA from degradation by DNases which are contained in the sample fluid. After performing the bead beating, impurities are removed from the sample by precipitation with ammonium acetate. The nucleic acids are obtained by precipitation with isopropanol. In a further method step the DNA is digested sequentially with RNase and Proteinase K and subsequently purified by means of a column.
The method has the disadvantage that it is relatively complex. Since the sample fluid is diluted by the adding of the buffer, the DNA concentration in the sample decreases. Therefore, the method allows only a limited detection accuracy and sensitivity.
Thus, there is a need for improved devices and methods for lysing cells and extracting nucleic acids from microorganisms contained in a sample fluid.